1. Field of the Invention
The present invention relates to a device fabrication method for dividing a wafer into individual devices along a plurality of crossing streets formed on the front side of the wafer, wherein the devices are respectively formed in a plurality of regions partitioned by the streets and the back side of each device is covered with an adhesive film for die bonding.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing streets (division lines) are formed on the front side of a substantially disk-shaped semiconductor wafer to partition a plurality of regions where devices such as ICs and LSIs are respectively formed, and these regions are separated from each other along the streets to thereby produce the individual devices. As a dividing apparatus for dividing the semiconductor wafer into the individual devices, a cutting apparatus called a dicing apparatus is generally used. The cutting apparatus includes a cutting blade having a thickness of tens of micrometers for cutting the semiconductor wafer along the streets. The devices thus obtained are packaged to be widely used in electric equipment such as mobile phones and personal computers.
An adhesive film for die bonding called a die attach film having a thickness of 20 to 40 μm is mounted on the back side of each device, and each device is bonded through the adhesive film to a die bonding frame for supporting the device by heating. The adhesive film is formed of epoxy resin, for example. The adhesive film for die bonding is mounted on the back side of each device by a method including the steps of attaching an adhesive film to the back side of a semiconductor wafer, attaching the semiconductor wafer through the adhesive film to a dicing tape, and cutting the adhesive film with the semiconductor wafer along the streets formed on the front side of the semiconductor wafer by a cutting blade, thereby forming the individual devices, wherein the adhesive film is mounted on the back side of each device (see Japanese Patent Laid-open No. 2000-182995, for example).
In recent years, it has been desired to further reduce the weight and size of electric equipment such as mobile phones and personal computers, so that thinner devices have been required. As a technique of dividing a wafer into thinner devices, a so-called dicing before grinding process has been put to practical use. This dicing before grinding process includes the steps of forming a kerf (dividing groove) having a predetermined depth (corresponding to the finished thickness of each device) along each street on the front side of a semiconductor wafer and next grinding the back side of the semiconductor wafer to expose each kerf to the back side of the semiconductor wafer, thereby dividing the semiconductor wafer into the individual devices. By this dicing before grinding process, the thickness of each device can be reduced to 50 μm or less.
However, in the case of dividing the semiconductor wafer into the individual devices by the dicing before grinding process, the kerf having a predetermined depth is formed along each street on the front side of the semiconductor wafer and the back side of the semiconductor wafer is next ground to expose each kerf to the back side of the semiconductor wafer. Accordingly, an adhesive film for die bonding cannot be preliminarily mounted on the back side of the semiconductor wafer. Therefore, in bonding each device fabricated by the dicing before grinding process to the die bonding frame, a bonding agent must be inserted between each device and the die bonding frame. As a result, a bonding operation cannot be smoothly performed.
To solve this problem, there has been proposed a semiconductor device fabrication method including the steps of mounting an adhesive film for die bonding to the back side of a semiconductor wafer divided into individual devices by a dicing before grinding process, attaching the semiconductor wafer through the adhesive film to a dicing tape, and applying a laser beam from the front side of the semiconductor wafer through the spacing between the adjacent devices to the adhesive film, thereby melting and dividing the adhesive film along the spacing between the adjacent devices to obtain individual adhesive films respectively mounted on the individual devices (see Japanese Patent Laid-open No. 2002-118081, for example).
According to the technique disclosed in Japanese Patent Laid-open No. 2002-118081 mentioned above, the laser beam is applied from the front side of the semiconductor wafer to the adhesive film mounted on the back side of the semiconductor wafer through each kerf formed by a cutting blade having a thickness of tens of micrometers, thereby melting and dividing the adhesive film at its portion exposed to the spacing between the adjacent devices. Accordingly, it is difficult to melt and divide only the adhesive film along each kerf without applying the laser beam to the front side of each device. Furthermore, in the step of attaching the semiconductor wafer divided into the individual devices through the adhesive film to the dicing tape, there is a possibility of meandering of each kerf, causing the difficulty of application of the laser beam along each kerf. Thus, the semiconductor device fabrication method disclosed in Japanese Patent Laid-open No. 2002-118081 mentioned above has a problem such that the laser beam may cause damage to the front side of each device.
Further, the technique disclosed in Japanese Patent Laid-open No. 2002-118081 has another problem such that the adhesive film is melted by the laser beam to cause adhesion to the dicing tape. Accordingly, there is a possibility that each device with the accompanying adhesive film cannot be peeled off from the dicing tape in a pickup step.